Hamster as a Model for Comparative Oral and Skin Wound Healing Oral wounds are known to heal effectively and more rapidly than similarly sized skin wounds. The cellular and molecular mechanisms responsible for these differences and presently not understood. Using the hamster skin as a model for wound healing, we have previously show that eosinophils are the majors cellular sources of TGF-a and TGF-b1, two cytokines of key importance in wound healing (Wong et al., J. Dent. Res. 71: 260 Abst. 1234, 1992). This study examines a site overlying the hamster masseter muscle for use in comparative studies of oral and skin wound healing at the cellular and molecular level. Seven mm circular wounds were created in oral mucosa of fifty male hamsters at the site overlying the masseter muscle. Oral wounds from five animals were harvested daily until day 8. Each harvested wound was processed for histology to examine eosinophil infiltration and in-situ hybridization to examines the expression of TGF-a and TGF-b1 mRNAs, using hamster-specific 35s- labeled TGF-a and TGF-b1 riboprobes. All oral wounds were clinically closed by day 5, compared to 14 days for similarly sized wounds. Eosinophils were seen to infiltrate prominently into oral mucosal wounds, peaking between day 3-4, compared to day 9-11 for skin wounds. Interestingly, unlike skin wound eosinophils which express mRNA for both TGFs, eosinophils in oral wounds were found to synthesize only TGF-B1 mRNA. The lack of TGF-a expression by oral wound-associated eosinophils maybe due to EGF and TGF-a normally present in saliva. We conclude that the mucosal site at the hamster masseter muscle is suitable for oral wound healing studies. Furthermore, this site can be used to investigate the cellular and molecular mechanisms responsible for the effectiveness and rapidity of oral mucosal healing. Key Words: eosinophil, hamster, TGFs, wound healing